Low back pain (LBP) is a common and costly public and occupational health problem that has been associated with the performance of repetitive lifting tasks in the workplace. Identifying better lifting strategies and training workers and low back pain patients in these strategies could serve to reduce the incidence LBP. The objective of the proposed study is to compare the effects of different lifting strategies on lumbar mechanics (in particular mechanical efficiency) during a lifting task. The long-term goal of our research is to identify safe lifting mechanics and improve rehabilitation approaches for correct body mechanics during lifting in people with LBP. This study will focus on developing a better understanding of the potential role stretch-shortening cycles may play in lumbar mechanics during a lifting task. Stretch-shortening has been shown in a number of repetitive and cyclic movements (running and jumping) to improve mechanical efficiency of the movement. The role of the stretch-shortening in the low back has not been examined. Lumbar-pelvic coordination studies, including preliminary studies by the authors, have shown patterns of hysteresis that would be consistent with a stretch-shortening mechanism. While stretch-shortening may improve mechanical efficiency, making lifting easier, it also will result in eccentric muscle contraction and spine flexion that could cause injury. In this study, the existence and role of stretch-shortening in lumbar mechanics will be investigated. We will investigate the mechanical efficiency of cyclic lifting tasks with different lumbar-pelvic coordination strategies (pelvis-first (high lumbar flexion), neutral, and pelvis-last (low lumbar flexion)). We will also examine the self- selected coordination patterns of novice and experienced lifters. It is hypothesized that those with experience in weight lifting for exercise will preferentially select a more neutral lifting strategy to avoid injury, even though it is less energy efficient. If this research is successful, future research goals will be to take these ideas into the clinical setting and investigate whether training LBP patients to avoid stretch-shortening coordination patterns and helping them build the endurance to be able to use other coordination patterns might help prevent recurrence of LBP injuries.